Patient positioning systems are used for accurate and reproducible positioning of a patient for radiation therapy, diagnostic imaging, surgery, and other medical procedures. During these procedures, it is important to immobilize a part or parts of the patient's body. Accurate positioning of the body part is also important in repeat treatments so that the precise same location of the bodies are exposed to the radiation each time. Therefore, different types of devices have been made to immobilize body parts and to index the body to the treatment table to assure proper and repeatable alignment for radiation therapy.
One example of such a patient positioning system is the Exact Indexed Immobilization system sold by applicant, and described in U.S. Pat. No. 5,806,116. The Exact system utilizes a tabletop with indentations along opposite sides, and a lock bar extending across the tabletop with a disk at each end adapted to be received in opposing indentations. The Exact lock bar is secured to the tabletop with an eccentric cam which tightens the ends of the bar into engagement with the indentations of the tabletop.
While the Exact system is generally an acceptable product, there are features causing potential concern. For example, the rotation of the cam lever causes the bar to move slightly relative to the tabletop, such that the patient positioning is not precise and consistent. Also, the Exact lock bar utilizes an O-ring on each end of the bar, which is not resistant to radiation. Therefore, over time, the O-ring may degrade to a degree wherein the bar does not mount as securely to the tabletop. The O-ring may also ultimately fail due to repeated and extensive exposure to the radiation. Furthermore, the thermoplastic patient fixation or restraint devices normally used in patient positioning systems tend to shrink over time, as a result of the initial heating and molding of the thermoplastic. Such shrinkage ultimately may lead to bending of the Exact bar when the restraint is forced downwardly over the patient. Such bending of the bar may lead to migration of the bar out of the tabletop notches. Also, patient swelling may impart stresses on the Exact bar which may preclude secure attachment of the bar to the tabletop or Exact repeatable positioning of the bar.
Therefore, a primary objective of the present invention is the provision of an improved patient positioning system for radiation therapy treatment.
Another objective of the present invention is the provision of a patient positioning system which is repeatably precise and accurate.
Another objective of the present invention is the provision of a patient positioning system which provides secure interlocking connection between the lock bar and the tabletop.
A further objective of the present invention is the provision of a patient positioning system which is easy and simple to use.
Another objective of the present invention is the provision of a patient positioning system which is durable in use and economical to manufacture.
These and other objectives have become apparent from the following description of the invention.